There remains a critical need to develop new safe and effective antiviral agents active against human pathogens, including herpes simplex virus (HSV) and human cytomegalovirus (CMV). The broad long term objectives of this project are to identify, characterize, overexpress, and exploit targets for such drugs. The project takes a combined approach to drug development in which advantageous elements of traditional drug development approaches are combined with modern approaches. Drug targets are identified using resistance to previously existing drugs, the drug targets are characterized molecularly and overexpressed, and the information gained is used to design and screen new compounds. The first specific aim is to develop novel drugs that inhibit the interaction of the HSV UL42 protein with a well-established target, the HSV DNA polymerase catalytic subunit (Pol). The structure of a region of Pol critical for its interaction with UL42 will be solved and drugs designed using the structure. Peptides derived from this region and from the interacting portion of UL42 will be used to develop peptidomimetic analogues. RNA aptamers and high-throughput screens will also be investigated. These routes to drug development will be supported by multidisciplinary approaches to protein-protein interactions. Information gained may be relevant to similar interactions in other clinically important systems. The second specific aim is to develop new drugs that target the CMV UL97 protein, which appears to be a protein/ganciclovir kinase. Overexpressed protein will be purified for structural studies. Protein and peptide substrates will be identified and used to derive peptide inhibitors. Screens for inhibitors of UL97 activities will be developed. These studies will be supported by molecular genetic analyses of UL97 and its role in CMV infection. The third specific aim is to identify novel drug targets of HSV and CMV by mapping mutations that confer resistance to drugs that appear to act selectively against these viruses by unknown mechanisms. These include certain nucleoside analogues and phosphorothioate oligonucleotides. These studies have the potential to identify exciting new drug targets, which could then be exploited much as Pol/UM2 and UL97 will be.